Plasma pleases plenty

Technological developments in lasers are positioning them as an attractive alternative to plasma. But fabricators are still sticking with plasma cutting for many applications where speed and cost-effective operation are concerns.

In case you missed it, check out this excerpt from the article "National research programs explore plate welding for shipbuilding" in the March 2004 issue of The FABRICATOR®:

One project objective is to introduce laser cutting technology—which is already being used to cut sheet metal worldwide and to cut plate in the Asian and European shipbuilding industries—to the U.S. shipbuilding industry for plate cutting The 6-kW Tanaka LMXIII CO2 laser from Alabama Laser used for the test project cuts mild steel plate 1.25 inches thick and as wide as 13 feet The laser-assisted oxygen cutting project group aspires to develop a laser technique that can cut plate as thick as 4 in. using relatively low power (less than 2 kW).

Of course, the improvement of laser cutting over the years is not really front-page news. Fabricators have gravitated toward the technology as it has become more affordable over the years and repeatable cut quality continues to remain hard to beat by more traditional technologies.

What is news is that laser cutting appears to be entering new territory—continual cutting of steel plate thicker than 1 in.—and further research promises to expand the territory even farther.

Where does this leave plasma cutting? Right where it's been for most of the past decade: a cost-effective, efficient means of slicing through sheet metal and plate that promises to be around for a long time thanks to some noteworthy technological developments.

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"A trend that we have seen is that companies have purchased lasers to do thicker materials on all of their production," said Derek Weston, sales and marketing manager for AKS Inc., a manufacturer of CNC plasma cutting machinery. "As they try to cut costs and when they see that their capacity is 'maxxed' out on a laser and they are processing thick material at very slow speeds, they are looking to replace those lasers with a high-density plasma system.

"That's an area where a company will accept the quality [that plasma cutting machines] offer, and it makes sense to replace the laser."

Speed Merchant

J.O. Mory Inc., a northern Indiana-based heating, ventilating, and air-conditioning contractor (HVAC) with a specialty fabrication division, recently has had work sent its way from a nearby metal fabricator, which happens to use a laser. The fabricator can laser-cut good parts, but it is running at full capacity, according to John Wilson Jr., J.O. Mory's weld shop foreman. Wilson figured his company's new Vicon plasma table is more than capable of taking on the extra work because of the machine's speed, which he estimated to be 10 times faster than the other company's laser machine.

New technology developments makes the speed possible. Previously the company used a 10-year-old Cybermation to plow its way through steel sheet and plate.

Several factors contribute to the increased speeds of plasma cutting equipment. First, several advancements have been made in the plasma torch source. The HySpeed® plasma cutting system from Hypertherm illustrates this point. In more traditional plasma cutting operations, the plasma gas runs between an electrode and the nozzle, gets ionized, and is hit with an electric current to create an arc. A shield gas, fed into the plasma arc at a right angle, helps to constrict the arc and cool the nozzle. With Hypertherm's Coaxial-assist™ approach, the shield gas is fed parallel to the plasma arc. David LaPrade, the team leader for Hypertherm's mechanized business, said this creates a faster and more powerful plasma jet.

The advancements don't end there. Microprocessors now control power supplies, which ensure proper power for specific jobs. Consumables are designed for and more aligned with higher amperages and precision cutting.

Software developments also have helped push the speed envelope. Operators don't need to spend as long with part entry thanks to improved user interfaces, and the actual time to do the initial programming is less. In some instances, the nesting and computer-aided design functions can be found in the same software package.

J.O. Mory's Wilson said the software—developed by the same company that manufactured the Vicon plasma cutter, Plasma Automation—really helped to sell them on the equipment purchase. He estimated that only two days are needed to train an operator to use the plasma cutter to do HVAC work because of the software programming that already exists.

"It's the programming capabilities that are exciting. Some of the people here in the company don't believe what they can do," Wilson said.

Quality Counts

Bill Kirkpatrick Jr., vice president of human resources and safety for custom fabricator NORFAB, was involved heavily in the purchase two years ago of its plasma cutting machine, an InnerLogic torch unit through AKS Inc. NORFAB, a sister company of Northern Ohio Roofing & Sheet Metal Inc., had an older plasma cutter, but the customers had newer quality expectations that the equipment couldn't meet.

"The older table at the time that we bought it was really more or less used to make fittings and ductwork. We really didn't need that much accuracy to do that," Kirkpatrick said. "But nowadays all of the customers are demanding a more finished product, and we are definitely able to achieve that with the newer technology."

The metal fabricator uses its plasma cutter on mild steel, stainless steel, and aluminum up to 1 in. thick.

"They've really perfected [the technology] quite a bit—a lot less dross than the older machines, a lot higher accuracy, and a lot smoother edge," Kirkpatrick added. "I think they have learned to utilize the gases better in the cutting process."

The industry is very clear about the applications in which gases should be used. For example, oxygen plasma has emerged as the industry standard because of its ability to help produce a good cut quality and to increase cutting speeds, but air plasma can be used in many instances on carbon steels if the quality requirements are not as stringent. Indeed, older nitrogen plasma systems are being used to produce acceptable cuts on stainless steel and aluminum. In some instances, multigas plasma systems are offered to give the end user choices when it comes to cutting.

But the quality improvements don't end with gas delivery. Brad Johnson, Koike Aronson's product manager of cutting equipment, pointed out that plasma equipment manufacturers are working closely with CNC manufacturers to develop features that help increase quality. An example of this is advanced torch height control.

Imagine a plasma torch head moving over an uneven surface. The torch head moves, mimicking the inconsistencies in the metal. The cut and impact on material are consistent throughout the process. Fabricators are taking advantage of this feature to produce better cuts not only on not-quite-perfect steel sheet, but also sheet with special features, such as diamond plate.

CNCs also can be retrofitted to older machines. The newer packages offer better programming features, faster communications, and a more user-friendly design.

For those fabricators who want a PC interface, they are finding machine control software that is also contributing to better cut quality.

"The improvements in fabricator cutting software offer better control of torch lead-in, lead-out, and kerf allowance. This better control of the cut path minimizes the number of material pierces, which in turn leads to longer consumable life and greater cut part accuracy," said Tom Barney, part of Plasma Automation's technical support staff.

Despite the strides made in quality, when it comes to plasma cutting, the technology's reputation is not as positive as it should be, according to Al Julian, marketing manager for W.A. Whitney Co.

"The tendency of the industry is to refer to parts as having 'laser quality' or 'plasma quality.' This does not allow for the various levels of distinction within the plasma cutting category," he said. "Some of today's high-definition, high-performance, and conventional oxygen plasma cutting systems rival laser cutting in terms of quality, but unfortunately, these processes do not receive the credit they deserve based on the performance of their less expensive cousins."

To illustrate the point, Julian noted that some plasma cutting tables do not have the same construction as laser cutting tables. Because the frames, drives, and gantries are not sized to offer crisp acceleration and deceleration, extra vibration during the cutting process creates more rounded parts. In the end, Julian said, the process gets blamed for the bad parts and not the equipment.

New Life

Fabricators like plasma cutting because for many it's affordable. They don't have to look too far to find a table for $15,000.

With this in mind, equipment suppliers are doing their best to prolong consumables life. Fabricators want the low cost of operation that they expect from a cost-effective piece of equipment.

For example, Hypertherm has incorporated something it calls LongLife® technology into its consumables. Flow technology at the torch and increased control of the power supply reportedly help to extend consumable parts life. Koike Aronson's Johnson said that InnerLogic is doing its own work on consumables in an effort to improve quality.

For some, however, the advancements are not yet an enticement to invest in the new technology.

Kyle Cloman is owner/president of Waste Gas Fabricating Co. in Fairless Hills, Pa. He bought a 200-amp 3400 XP punch/plasma machine from W.A. Whitney almost two years ago. The company processes steel from thin gauges all the way to 12-in.-thick plate.

Waste Gas ran a demo almost a year ago testing new consumables. Cloman said they were impressed, but the price remained a stumbling block.

Sometimes the perception of higher operating costs associated with plasma cutting is not warranted. Consumables life may be greatly reduced if plasma cutting is not the appropriate technology for a certain application, according to W.A. Whitney's Julian.

A simple rule of thumb, Julian said, is that the life of a plasma cutting consumable is related to the number of times the arc is initiated. So for hole-intensive work, the operating cost per part goes up based on the number of holes that need to be created on each part. Each time a hole is created, the arc has to be reignited.

Just One Answer

In the end, plasma cutting still has a place in many fabricating shops. Lasers have made strides, but so have plasma machines.

But as customer requirements grow more demanding, the equipment mix grows more varied. The days when a fabricator cut metal exclusively with plasma may be past.

NORFAB has a waterjet on the same gantry as its plasma cutting torch. "We really bought the equipment because it had both capabilities," said NORFAB's Kirkpatrick.

"What we were looking at [prior to the equipment purchase] was that everyone was purchasing lasers. We didn't want to get into that market. We wanted to be able to achieve similar tolerances with the plasma that would meet our customers' demands," he added. "With the waterjet, we are able to carry that to the next level."

With the waterjet, NORFAB can cut almost any material other than tempered glass. Kirkpatrick said the equipment's maximum cutting thickness is 7 in.

Waste Gas Fabricating doesn't have a waterjet, but it does offer a Bystronic 4,000-watt laser, two Messer MG plasma/flame machines, and a Messer MG dual plasma cutter to go along with its W.A. Whitney punch/plasma combination unit.

"If we are cutting for the refuse industry, they don't need laser-cut [metal] to build roll-off cans, so we are going to cut that metal with a plasma head. It's fast and quick," Waste Gas' Cloman said.

By the sound of it, few fabricators are ready to abandon ship when it comes to plasma cutting technology.

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The Fabricator®

The FABRICATOR® is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971. Print subscriptions are free to qualified persons in North America involved in metal forming and fabricating.